There has previously been proposed (in Japanese Patent Application No. 31937/1981) machining equipment for machining the valve seat surface in a cylinder head of an internal combustion engine, which includes a rotating body or reamer carrying thereon machining tools and rotatable about an axis not coaxial with or out of alignment with its driving shaft.
The construction and function of such proposed machining equipment will be preliminarily described hereinbelow with reference to FIGS. 6 and 7 of the accompanying drawings.
The reference letter M generally designates an overall machining apparatus. At a central part of the machining apparatus M, a tool holder a provided centrally with a reamer l for finishing a guide bore of a valve stem guide g and also provided on the outer periphery of its central part with cutting tools c such as cutters for machining a valve seat V.sub.S is bendably connected to a spindle s through a universal joint j. On the other hand, guide bars G extend forwardly from a multiple spindle head H, and a ring-like support plate P is slidably suspended from the guide bars G. On the front surface of the support plate P there is slidably disposed a tubular bearing holder d which accommodates a self-aligning bearing b fixed to the inside of its front end portion, and a flange portion of the holder d is held by a locking plate f having locking cylinder e. In the machining operation, the multiple spindle head H is advanced while rotating the spindle s, thereby allowing the reamer l to catch the guide bore of the valve stem guide g and to move forwardly while following the guide bore as shown in FIG. 7, and in the course of this movement the tool holder a is allowed to fit in the self-aligning bearing b so that changes in inclination of the tool holder a can be absorbed by the aligning action of the self-aligning bearing b and by the sliding of the bearing holder d. When the reamer l has advanced up to the position in which it finishes following the guide bore, the locking cylinders e are actuated, allowing the respective piston pins to fix the bearing holder d in a certain state with respect to the support plate P. Thus, in a state wherein the front and rear positions of the cutting tools c are borne by the valve stem guide g and the self-aligning bearing b, respectively, the valve seat surface is machined by the cutting tools c while maintaining a high roundness and a good concentricity with respect to the guide bore.
In the above machining apparatus, however, the outside diameter of the bearing holder d incorporating the self-aligning bearing b becomes relatively large and its weight is substantially increased, so that after the tool holder a fits in the self-aligning bearing b during the forward movement of the reamer l and before it is fixed to a certain state, the weight of the self-aligning bearing b and that of the bearing holder d are imposed on the tool holder a, and in this respect there has been room for further improvement. Moreover, the inner surface of the self-aligning bearing b comes to move in the axial direction while the tool holder a is fitted therein, therefore a highly accurate clearance is needed, and thus also in this respect there has been a room for further improvement.